Comment 3 for bug 1387328

What breaks this is inserting the overlay between the treeview and it's scrolledwindow. Putting the overlay outside makes it work.

I tried to fix this in the code by adding one more level of .getparent() in add_spinner_over_treeview, but simply removing the scrolledwindow and adding it back moves the details to the bottom of the vbox, putting the checkboxes above it. Not nice. So instead of that I moved the Gtk.Overlay() into the .ui file.

(I attempted to also move the spinner to the .ui file but failed miserably: the tree view stopped receiving mouse events as soon as I put a <child type="overlay"> with the spinner. And since moving everything to the .ui made the patch bigger, I gave up and went with the smaller change.)